When synthesizing engineered nanomaterials (ENMs), surface coatings are applied to prevent their aggregation and impart specific functionality (e.g., targeted drug delivery). These surface coating also influence the fate of ENMs in aquatic environments by mediating the adsorption of natural organic matter and altering interactions with suspended particulate matter. To investigate this phenomenon, researchers typically use ‘pristine’ ENMs that are representative of their ‘as-produced’ form. However, it is unlikely that ENMs released to the environment will resemble their ‘pristine’ state. Instead, the physiochemical properties of ENMs will be altered through a variety of processes during their life-cycle. Engineered systems, such as sewers and wastewater treatment plants, represent one such life-cycle stage where ENM properties can be transformed (termed ‘aging’) prior to their incidental discharge to the environment.  The aim of this study was to compare the aggregation behavior of ‘pristine’ and ‘aged’ ENMs in samples of raw and filtered river water. Gold nanoparticles (AuNPs) coated with polyethylene glycol (PEG), lipoic acid (COOH) and branched polyethylenimine (bPEI) were selected as model ENMs. Using a previously reported technique, the AuNPs were aged in filtered primary wastewater. During this aging process, the physiochemical properties of the AuNPs were altered via aggregation and the acquisition of an organic matter corona. When added to river water, only two AuNP types in their pristine form were removed to a significant extent via aggregation and settling (PEG-AuNPs in raw river water and COOH-AuNPs in filtered river water). This indicates that the physiochemical properties of the pristine AuNPs influence ENM behavior in river water, generally preventing their homo- and/or heteroaggregation. After aging, all the AuNP types underwent aggregation in the raw and filtered river water. Higher removal was observed in the raw river water compared to filtered river water, demonstrating that the aged AuNPs undergo heteroaggregation in addition to homoaggregation. Negligible removal of the aged AuNPs was observed in ultrapure water, revealing that the aging of ENMs in wastewater stimulates their aggregation and subsequent removal in natural aquatic systems. It is hypothesized that the impact of the initial engineered surface coatings on the environmental fate of ENMs is largely masked by subsequent corona formation in wastewater treatment systems.

Comparing the fate of pristine and wastewater-aged gold nanoparticles in freshwater: Impacts of surface coating functionality

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.